The physical adsorbent-based gas storage and dispensing system disclosed in Tom et al. U.S. Pat. No. 5,518,528 has revolutionized the transportation, supply and use of hazardous gases in the semiconductor industry. The system includes a vessel holding a physical adsorbent medium such as molecular sieve or activated carbon, having sorptive affinity for the gas that is to be stored in and selectively dispensed from the vessel. The gas is held in the vessel in an adsorbed state on the sorbent medium at reduced pressure relative to a corresponding empty (of sorbent) vessel holding an equivalent amount of gas in the “free” (unadsorbed) state.
By such reduced pressure storage, the safety of the gas storage and dispensing operation is substantially improved, since any leakage will result in a very low rate of egress of gas into the ambient environment, relative to a conventional high pressure gas storage cylinder. Further, the low pressure operation of the adsorbent-based system is associated with a lower likelihood of such gas leakage events, since the reduced pressure reduces the stress and wear on system components such as valves, flow controllers, couplings, joints, etc.
In such adsorbent-based gas storage and dispensing systems, the working capacity of the physical adsorbent medium is an operating constraint. The working capacity is the amount of gas that can be stored (“loaded”) on the sorbent medium and desorptively removed from such sorbent medium for use. The working capacity is a function of the storage pressure of the gas in the sorbent medium-containing gas storage vessel, and the dispensing condition of the desorbed gas (e.g., dispensing pressure of the desorbed gas, when pressure differential is used to effect desorption, and temperature levels of respective storage and dispensing conditions, when thermal desorption of gas is used as the dispensing modality), and the type and character of the sorbent medium itself (e.g., involving such parameters as sorbent media size, shape, porosity, pore size distribution, and tortuosity of interior pore passages).
The art is continually seeking improvement in working capacity of the physical adsorbent-based gas storage and dispensing system.